Cellular events typically require precise regulatory control. Regulation failures may lead to problems like uncontrolled cellular proliferation and cancer. The regulation of spermiogenesis in the model nematode Caenorhabditis elegans is the focus of the proposed research, and it has the potential to provide insight into the workings of genes homologous to those involved in Alzheimer's disease and to aid in understanding regulated vesicle exocytosis, an event important in neuronal function and muscle membrane repair. During spermiogenesis, the spherical spermatid undergoes a dramatic reorganization to form an amoeboid spermatozoon. Spermiogenesis involves cytoskeletal and membrane reorganization and vesicle exocytosis, yet it occurs without new gene expression, employing only preexisting cellular components. As with other cellular systems, the regulation of spermiogenesis in C. elegans involves both positive and negative controls, but the negative regulation that inhibits spermiogenesis is poorly understood. The research proposed here will characterize the genes involved in spermiogenesis inhibition by examining a collection of ten mutants that fail to inhibit spermiogenesis properly. Preliminary data indicate that three of the mutations in this collection map to unique loci that do not correspond to known sperm genes. These mutations define genes involved in spermiogenesis inhibition, and the aims of the proposed research are to: (i) identify and clone the spermiogenesis inhibition genes in this collection;and (ii) characterize the functions of the identified genes. To accomplish these aims the mutations will be genetically mapped using molecular and morphological markers. The coding sequence affected by at least two, but perhaps as many as four of the mutations will be identified using a combination of approaches that include DNA sequencing, transformation rescue, and complementation tests. Phenotypic, genetic, and bioinformatic analyses will provide information on the mechanism of action for the gene products. The proposed research is significant because it will enable both a comprehensive understanding of the regulation of spermiogenesis in C. elegans specifically and a better understanding of vesicle exocytosis in general. Indeed, the mutant collection to be studied here has already been fruitful in providing information on the human neurodegenerative disease gene homolog spe-4 (Alzheimer's disease), showing it inhibits spermiogenesis. Public Health Relevance: The regulation of spermiogenesis in C. elegans has very significant relevance to human health. Because spermiogenesis shares characteristics with regulated vesicle exocytosis in humans, the proposed research will aid in understanding regulated exocytosis. In addition, this research has the potential to provide insight into the workings disease gene homologs, such as spe-4 (Presenilin-1;Alzheimer's disease) and fer-1 (Dysferlin family genes;muscular dystrophy).